Two preliminary findings served as the impetus for this research program. Over-eating was observed in normal, intact animals offered a complete diet and a palatable caloric solution. Obesity occurred as result of this over-eating in adult rats but these additional calories did not influence the rate of weight gain in young, rapidly growing animals. These data appear to have many parallels to the conditions associated with adult - onset obesity in man. The objective of the proposed research is to extend the generality of these initial observations and to examine the influence of other carbohydrate sources, dietary balance, exercise and sex differences on this phenomenon. This research will also begin to define the physioloical and behavioral characteristics of these obese animals by studying whether these elevated body weight levels are defended in response to environmental and physiological regulatory challenges.